1,2-epoxides are valuable intermediates, especially when the molecule contains a second functional group. Thus, epoxides as a whole are a very important class of compounds as starting materials for polymers and as intermediates in the organic synthesis. Conventionally, these epoxides are prepared with the use of epichlorohydrin.
The catalytic oxidation of olefins by hydrogen peroxide has seen increased patent activity and has drawn quite some academic interest, although actual use of these oxidation reactions has not seen a commercial follow-up.
For instance the process for the manufacture of epichlorohydrin (“ECH”) in WO2004/048353 is carried out in a reaction medium comprising at least 75% w of organic material, causing significant isolation problems.
As mentioned above, epoxidation of terminal or electron-deficient olefins with hydrogen peroxide catalyst by manganese catalysts has been extensively described in the public art, but typically using acetonitrile as reaction medium. An example of such a paper is Tetrahedron Letters 43 (2002) 2619-2622, with turnover numbers of up to 860. In the oxidation of ethylbenzene, in Journal of Molecular Catalyst A: Chemical 185 (2002) 71-80, a mixture of acetonitrile and water is used. In Journal of Organometallic Chemistry 520 (1996) 195-200 a series of manganese complexes are explored on their catalytic behavior using different solvents. Water was not studied. A heterogenized Mn catalyst has been described in Angew. Chem. Int. Ed., 1999, 38, No. 7, using acetone and acetonitrile as solvents. In Bull. Korean Chem. Soc., 2003, Vol. 24, No. 12, 1835 the alkane oxidation catalyzed by manganese tmtacn complexes with hydrogen peroxide is described, using acetone as solvent. The oxidation of saturated hydrocarbons is described in Russian Chemical Bulletin, Vol. 47, No. 12, December 1998, 2379, using acetonitrile as solvent. The oxidation of alkanes is performed in Inorg. Chem., 2007, 26, 1315-1331 in aqueous nitrile (50%) or in acetone as solvent. The epoxidation of dec-1-ene with hydrogen peroxide in the presence of a dinuclear manganese derivative carried out in a biphasic system provided no epoxide, but in the presence of a small amount of acetonitrile yielded epoxide with a TON of 373, see Journal of Organometallic Chemistry 690 (2005) 4498-4504. In Adv. Synth. Catal. 2002, 344, 899-905 a table is provided on systems based on Mn-TACN derivatives as catalyst for oxidations of organic compounds with hydrogen peroxide. The solvent typically is acetone or acetonitrile, albeit that water has been mentioned for bleaching of stains or oxidation of phenols, which is believed to generate a wide range of products but little or no epoxides. The conclusion of this paper once again seems to be that acetonitrile as a solvent is required. From the same author, G. B. Shul'pin et al, there are a number of papers with the same conclusion on acetonitrile as solvent (Journal of Molecular Catalysis A: Chemical 222 (2004) 103-119). In the paper Inorg. Chem. 1996, 35, 6461-6465 the activity of new manganese catalysts was described towards olefin oxidation with hydrogen peroxide. Interestingly, the olefin oxidation studies showed that oxidation reactions in aqueous solutions of water-soluble olefins did not necessarily result in the corresponding epoxide. For instance, diols were produced when the corresponding epoxide was not sufficiently stable under the reaction conditions. This, however, is not problematic at all if the purpose of the reaction is to bleach stains and either discolor and/or remove contaminants from fabrics by improving their solubility. The mechanism of bleaching has in fact been further studied in Journal of Molecular Catalysis A: Chemical 251 (2006) 150-158. Thus, in alkaline aqueous solutions, typically employed in detergents, the dinuclear species used as catalyst yields lignin oxidation. Again, it should be noted that this process does not seem to be one suitable for actually producing epoxides.
A fairly early paper on the topic of epoxidation suggests the use of water as a solvent; see Tetrahedron Letter 39 (1998) 3221-3224, but all reactions are actually carried out in acetonitrile.
Whether epoxides may be manufactured in water as a solvent, and moreover in high turnover numbers therefore remains unclear.
In EP0618202 the epoxidation of olefins via certain manganese complexes is described. The method is said to include a step of recovering epoxidized olefin. According to this reference, epoxidation is best conducted in a fluid medium, especially an aqueous system. When the epoxidation is conducted in an aqueous medium, it is said that the best results are obtained on olefins with water-soluble groups such as those with carboxylate and hydroxyl units, e.g., vinylbenzoic acid, styrylacetic acid, and hexenoic acid which are all fully soluble in water. In addition to these water-soluble olefins also allyl alcohol is epoxidized using water as reaction medium. Allyl alcohol is completely miscible in water. A further listing of suitable olefins is provided, albeit that these are not the olefins to be used in an aqueous medium. The catalyst:olefin:hydrogen peroxide ratio in the examples is typically 1:100:10,000, which corresponds with the (preferred) ratio of oxidizing agent in relation to the olefin of from 500:1 to 20:1. Interestingly, no data is provided on the yield of epoxide, which rather suggests that the olefin is not only converted into the corresponding epoxide but also (or more so) in the corresponding diol, as might be expected on the basis of the academic studies reported on earlier in this specification.
From the above it is clear the industry is still looking for a commercially feasible process for the manufacture of 1,2-epoxides, in high turnover numbers and at high selectivity, meaning substantially free of byproducts such as diols. This process should also allow the use of an aqueous solvent as reaction medium, to avoid environmental and other problems related to acetonitrile and similar organic solvents. The present invention overcomes these disadvantages.